In a post apocalyptic covid-19 world, a small but violent robot forms a friendship with a human and is entrusted to transfer the only vaccine to the CDC headquarters.

Thanks! I’ll definitely lean towards that 👍

Dig it! Since there's an inherent spoiler - as we are on the verge of receiving a COVID-19 vaccine, I altered it to "disease".
Leaning towards:
"In a post-apocalyptic world ravaged by disease, a small but violent robot reluctantly sets out on a cross-country journey to deliver an experimental vaccine to CDC headquarters"

Take care.